Some mobile communication systems offer high data rate by employing multiple antenna systems utilising Multiple-Input and Multiple-Output (MIMO).
Massive MIMO (MMIMO) is a recently emerged technology that uses large Antenna Arrays Systems (AAS) with individual transceivers connected to one or several antenna elements to improve throughput of wireless communication systems. A Massive MIMO system may sometimes also be referred to as “very large MIMO system”, or “large-scale antenna system”.
Antenna arrays with large number of antenna elements and transceivers enable to be used in both downlink and uplink to increase capacity by utilising high spatial resolution with beam forming and spatial multiplexing. Both single user MIMO with many layers and multi user MIMO will increase the network performance and system capacity. The MMIMO system cost and power consumption is highly dependent on the operating bandwidth that the MMIMO system comprising the Radio Frequency (RF) transceiver need to support.
The Base Transceiver Stations (BTS), which in some networks may be referred to as “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and/or terminology used, are often equipped with a sector antenna and Remote Radio Units (RRU) that normally support one band and a Limited Bandwidth (LBW). The RRUs are connected to the antenna with a RF cable and for multi band solution also with a combiner or a diplexer.
For multi antenna solutions like MMIMO arrays the antenna and transceivers are placed in the antenna unit and can be tightly integrated. The cost and power consumption of the transceiver is highly dependent on the bandwidth that the transceiver needs to support. Thus, increased demands for bandwidth leads to increased power consumption and costs.
A conventional solution for supporting high bandwidth and multi band solutions is to add RRU and combine frequency bands to a single antenna or add another antenna. For high operating bandwidth (OBW) the RRU hardware needs to support higher bandwidth which is possible to solve within one frequency band to a high cost and power consumption.
Providing high bandwidth is a challenge for the transceiver and radio equipment involved, as the simultaneous support of high bandwidth makes the radio equipment more complicated and entails increased costs and power consumption.
For MMIMO solutions the dual bands are supported by band specific hardware, such as e.g. transceiver (TRX) and antenna array. For high OBW the TRX needs to support the entire OBW.
However, moving from single antenna systems towards MMIMO systems creates new problems and challenges that need to be solved, in order to reap the benefits. It appears that MMIMO requires further development for supporting higher OBW or higher dual band operation, than the RF transceivers maximum OBW.